Key goes into ignition with the greatest of ease. Sometimes wont start the car, sometimes will. Do i need a new ignition? Could this be expensive or maybe just something simple wrong? Car is 5 years old. thanks

so get a new ignition switch,if its bad it wont come up as a code

GM cars have bad problem with security system. If you key turn light and will start other time will stick and need shaking to turn over and won't start just replace the key. Security system need some times to refresh the memory.
1.turn key ON for 10min.
2.turn key OFF 10sec.
3.turn ON 10min.
4.turn OFF 10sec.
5.turn ON 10min.
turn OFF ON and start
total of 30 min. to refresh the memory
the next step is more expensive and need some skills.
on top of the ignition switch is a sensor go bad
replace ignition switch with the sensor and do the learning process from step 1 to 5

I would suspect you may have a defective ignition starter switch.

I WOULD GO AND GET NEW IGNITION SWITCH THEY TIEWAPPED OLD KID? YA I WOULD SAY START BY REPLACING SWITCH THE RIGHT WAY. THEN IS PROBLUM IS FIXED AND U WANT ONE KEY FOR ALL GO TO A LOCK SMITH SO HE CAN MACH UP TUMBLERS IN SIDE LOCK SO ONE KEY WORKS ALL

u shud hav auto scanned by a unit that runs a data stream to help target solution--just reading codes ina parts place is to general--sometimes may mean the key chip is bad or the ignition switch

Try spark plugs, they are a very common problem and will cause loss of performance hard starting, and engine failure. Inexpensive place to start troubleshooting

You need to reset the theft system. To do this, try to start it. It should start and die. Then after it dies and the theft light is flashing, leave the key on for 10 minutes. After 10 min, the theft light should go out. After the theft light goes out, turn off the key. Count to 5, then restart it. Then it should work.

sometimes when one replaces the ignition a small plastic part falls from the new ignition causing it not to fully engage-for fun turn key with a liitle firmness all the way to sart-sometimes with added pressure it engages-orthewise remove ignition for examination

You may have a starter or ignition switch issue. I would guess starter with just the information you are giving. Of course with electrical problems proper testing needs to be done to condemn expensive parts such as a starter.

sounds like ignition cylinder has gone bad, try sliding key in and out while turn key and if key slops around cylinder is bad